The measles outbreak centered in northwest Texas grew to 683 cases and spread to three new counties on Friday, according to health officials. The latest update from the Texas Department of State Health Services adds 20 new cases since the agency’s last update on Tuesday.

With two confirmed measles cases in Travis County and a large outbreak in West Texas, do you need a measles booster? Here's what to know.

The Centers for Disease Control and Prevention confirmed nearly 900 measles cases in the U.S. on Friday, though much of the measles cases in the country remain centered in Texas, which confirmed earlier this week there have been 624 cases of the highly contagious illness in the state this year.